Have you ever come back to your desk to discover that someone left a note on your chair? I am sure most office workers regularly encounter this situation. I believe the reason people leave notes on their colleague’s chairs is that they do not trust that person’s inbox.
The inbox is designed to capture new information and works best when new input is regularly processed and organized. Once an inbox fills with clutter, new input quickly gets lost. People see that messy inbox as a graveyard and avoid it like a real one. Therefore, they will find ways around the dysfunctional inbox and a favorite option is to use the chair. They assume that the person will see it before they sit down!
To avoid having your colleagues turn your chair into an inbox, try working the one on your desk more efficiently. Clean it out every 24-48 hours to stay fresh for new input. Be warned, some people are now programmed to bypass even a clean inbox and automatically go for the chair. When this happens to me, I tell that colleague that I will sit on the item, literally and figuratively. Then I politely point them to my inbox and ask that they place it there instead for timely processing. It keeps the chair much more comfortable that way.